In a method of making a thermoplastic film (which can also be referred to as a sheet, layer, foil, and the like), an extrusion system can be employed, wherein a thermoplastic plastic resin can be extruded through a screw extruder to form the thermoplastic film. The extruded thermoplastic film can be pulled by a pull roll and drawn under pressure between a first nip roll and a second nip roll, which can be independently driven by separate motors (e.g., driven by direct current (DC) electric motors). It is noted that roll speed fluctuations between the rolls can cause “ripples” to appear on the extruded thermoplastic film. Other factors that can cause ripples in the film include differences in the nip force between the rolls, differences in the film flow rates at the nip rolls and the pull roll, differences in roll speeds, and the like.
One application where ripples can be problematic is in an application where the thermoplastic film is used as an optical film (e.g., in compact disks (CDs), digital video disks (DVDs), light-management films for liquid crystal display (LCD) devices, eye glasses, windows panes, and the like). More particularly, ripples in the thermoplastic film can cause undesirable optical properties in the film (e.g., a decrease in luminance (e.g., brightness) and an increase in the percentage of haze), which can be tiring on the eyes of a viewer.
Accordingly, what is needed in the art is a method of making a thermoplastic film that minimizes and/or eliminates the appearance of ripples in the thermoplastic film.